Differential utilization by Haemophilus influenzae of haemoglobin complexed to the three human haptoglobin phenotypes

Haemophilus influenzae has an absolute requirement for heme, which may be supplied as the haemoglobin-haptoglobin complex. Utilization of haemoglobin-haptoglobin by H. influenzae is mediated by a family of proteins termed the haemoglobin-haptoglobin binding proteins (Hgps), of which a given strain may contain up to four genes. Human haptoglobin occurs in three phenotypes (1-1, 2-1 and 2-2). Using mutant derivatives of an H. influenzae type b strain that expressed single Hgps we analysed the ability of each Hgp to utilize haemoglobin complexed to the various haptoglobin phenotypes. A strain expressing only HgpB was able to utilize haemoglobin bound to all haptoglobin phenotypes significantly better than strains expressing either HgpA or HgpC.